Gateway request classification, compaction, and route ordering

Reject missing or header-less requests with HTTP 400 Malformed request: missing headers before authentication, routing, or admission. Then process gateway /lore:* commands, Claude Code side channels, structural compaction, and normal turns in that order. Commands and compaction never reach upstream; side channels and meta requests bypass LTM, distilled prefixes, and compaction classification. For compaction, restore the persisted project path before initIfNeeded() rather than binding a path-less probe to gateway cwd. Open Anthropic SSE immediately, emit ping keepalives throughout summary generation and 429 retries, and translate that canonical stream for OpenAI, Responses, and Gemini clients.